Module bypass switch for balancing battery pack system modules with bypass current monitoring

ABSTRACT

A battery pack system module may include a module bypass switch for allowing charge current to bypass the battery pack system module. The module bypass switch may be activated to divert charging current from the battery pack system module to other battery pack system modules. The charging current may be diverted to bring other battery pack system modules into balance with the battery pack system module. That is, to bring the state of charge of all battery pack system modules into coarse balance. When the module bypass switch is activated, charging current through the module bypass switch may be monitored by a current sensing device such as a current sensing resistor. A microprocessor may receive information about the bypass current level and use the information to determine when to de-activate the module bypass switch. Sensing current through a module bypass switch allows more accurate and quicker inter-module balancing.

PRIORITY CLAIM

This application is a divisional of U.S. patent application Ser. No. 13/494,502 to David A. White et al. entitled “Module Bypass Switch with Bypass Current Monitoring” filed on Jun. 12, 2012, which claims priority to U.S. Provisional Patent Application No. 61/498,358 to David A. White et al. entitled “Module Bypass Switch for Balancing Battery Pack System Modules with Bypass Current Monitoring” and filed on Jun. 17, 2011, all of which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure generally relates to a system for balancing a plurality of battery pack system modules.

BACKGROUND

A device powered by rechargeable batteries may include several battery cells to achieve the voltage and/or current levels used by the device. For example, if a rechargeable battery cell has a nominal output voltage of 1 Volt, the a device having a 2 Volt operational level may include two battery cells placed in series. In another example, if a rechargeable battery cell has a nominal output current of 100 milliamps, then a device having a 400 milliamp operational level may include four battery cells in parallel. Battery cells in parallel and series may be combined to reach the operational levels of the device.

The battery cells may be grouped with circuitry for balancing the charge levels in the battery cells to form a battery pack system module. Multiple battery pack system modules may be combined in series or parallel to further increase the output voltage and output current available to a device coupled to the battery pack system modules. Although battery cells within a battery pack system module may be balanced by using balancing circuitry within the battery pack system module (referred to as intra-module balancing), there is a need for balancing battery pack system modules to other battery pack system modules (referred to as inter-module balancing).

One conventional solution for providing inter-module balancing includes shorting out a battery pack system module within a battery pack system with a bypass switch. FIG. 1 is a block diagram illustrating a conventional battery pack system module with a bypass switch. A battery pack system 100 includes battery pack system modules 110, 130. The module 110 includes a first group of battery cells 114 having a battery cell 116 coupled in parallel with a battery cell 118. The module 110 also includes a second group of battery cells 124 having a battery cell 126 coupled in parallel with a battery cell 128. The first group 114 is coupled in series with the second group 124.

When a bypass switch 112 activates, current through the module 110 is diverted away from the battery cells 116, 118, 126, and 128. To prevent short circuiting of the battery cells 116, 118, 126, and 128, a resistor 120 is coupled in series with the switch 112. However, the resistor 120 consumes power and generates heat in the system 100 through Joule heating. The heat generated by the resistor 120 may result in dangerous conditions within the system 100. For example, the heat may lead to a fire involving the battery cells 116, 118, 126, and 128.

Heat generated by the resistor 120 may be problematic where the system 100 is operating in an isolated environment. For example, on an undersea vehicle such as a submarine, battery pack systems may be isolated in a pressurized compartment. Thus, heat dissipated by the resistor 120 may not be carried away and result in dangerous conditions for the vehicle and operator of the vehicle.

Additionally, when one of the modules 110 or 130 of the system 100 becomes defective, the defective module may be replaced with a new module. The new module may be at a significantly different charge than existing modules of the system 100. In a conventional system, balancing of the replacement module with the existing modules may occur over a long period taking days or weeks to reach balance. During this time the system 100 may be unavailable for use. In the above example if one module in the vehicle is replaced, the vehicle may not be ready for operation until the modules are fully-charged and balanced. If the balancing operation consumes days or weeks, the vehicle may be out of service for this entire time period.

Conventionally, current through a bypass switch of a battery pack system module is not monitored. However, monitoring the current may allow capture of information regarding other battery pack system modules without establishing a separate communications bus. The information obtained from other battery pack system modules may allow faster and more accurate charging of the battery pack system modules.

SUMMARY

According to one embodiment, an apparatus includes a first battery pack system module. The apparatus also includes a battery cell coupled between a first terminal and a second terminal. The apparatus further includes a charge switch coupled in series with the battery cell and the first terminal for interrupting charging of the battery cell. The apparatus also includes a discharge switch coupled in series with the charge switch and the first terminal for interrupting discharging of the battery cell. The apparatus further includes a module bypass switch for shorting the first terminal and the second terminal. The apparatus also includes a current measurement device coupled between the module bypass switch and at least one of the first terminal and the second terminal.

According to another embodiment, a method includes bypassing a charging current through a module bypass switch of a first battery pack system module without charging battery cells of the first battery pack system module. The method also includes monitoring the charging current through the module bypass switch of the first battery pack system module. The method further includes detecting, during the bypassing, that the charging current has fallen below a threshold value. The method also includes stopping the bypassing of the charging current through the module bypass switch of the first battery pack system module when the charging current has fallen below the threshold value.

According to yet another embodiment, a computer program product includes a non-transitory computer-readable medium having code to bypass a charging current through a module bypass switch of a first battery pack system module without charging battery cells of the first battery pack system module. The medium also includes code to monitor the charging current through the module bypass switch of the first battery pack system module. The medium further includes code to detect, during the bypassing, that the charging current has fallen below a threshold value. The medium also includes code to stop the bypassing of the charging current through the module bypass switch of the first battery pack system module when the charging current has fallen below the threshold value.

According to one embodiment, an apparatus includes a first battery pack system module. The module includes a battery cell coupled between a first terminal and a second terminal. The module also includes a charge switch coupled in series with the battery cell and the first terminal for interrupting charging of the battery cell. The module further includes a discharge switch coupled in series with the charge switch and the first terminal for interrupting discharging of the battery cell. The module also includes a module bypass switch for shorting the first terminal and the second terminal.

According to another embodiment, a method includes charging a first battery pack system module with a charging current. The method also includes detecting, during the charging, that the first battery pack system module has reached a first criteria. The method further includes stopping charging of the first battery pack system module after detecting the first battery pack system module has reached the first criteria. The method also includes stopping discharging of the first battery pack system module after detecting the first battery pack system module has reached the first criteria. The method further includes activating a module bypass switch to pass the charging current through the first battery pack system module without charging the first battery pack system module after stopping discharging of the first battery pack system module.

According to yet another embodiment, a computer program product includes a computer-readable medium having code to monitor a first battery pack system module. The medium also includes code to disable charging of the first battery pack system module when a first criteria is met. The medium further includes code to disable discharging of the first battery pack system module when a first criteria is met. The medium also includes code to enable passing charge current through the first battery pack system module when the first criteria is met. The medium further includes code to re-enable charging of the first battery pack system module when a second criteria is met.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily used as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features that are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, reference is now made to the following descriptions taken in conjunction with the accompanying drawings.

FIG. 1 is a block diagram illustrating a conventional battery pack system module with a bypass switch.

FIG. 2 is a circuit schematic illustrating an exemplary battery pack system module having charge, discharge, and bypass module switches according to one embodiment.

FIG. 3 is a block diagram illustrating an exemplary battery pack system having series and parallel coupled battery pack system modules according to one embodiment.

FIG. 4 is a flow chart illustrating an exemplary method of charging a battery pack system module according to one embodiment.

FIG. 5 is a block diagram illustrating an exemplary battery pack system having inter-module communication according to one embodiment.

FIG. 6 is a block diagram illustrating an initializer for an exemplary battery pack system according to one embodiment.

FIG. 7 is a flow chart illustrating an exemplary method of charging a battery pack system according to one embodiment.

FIG. 8 is a block diagram illustrating a software application for monitoring a battery pack system according to one embodiment.

FIG. 9 is a circuit schematic illustrating an exemplary battery pack system module having charge, discharge, and module bypass switch and bypass switch current monitoring according to one embodiment.

FIGS. 10A and 10B are a flow chart illustrating an exemplary method of charging a battery pack system module with bypass switch current monitoring according to one embodiment.

DETAILED DESCRIPTION

A battery pack system having a plurality of battery pack system modules may be inter-module balanced by including a module bypass switch, a charge switch, and a discharge switch in the battery pack system modules. A charge switch within the battery pack system module may be used to prevent charge current from passing through the battery cells of the battery pack system module. When one battery pack system module of a battery pack system is unbalanced with other battery pack system modules of the battery pack system, the module bypass switch may be activated to allow charge current to bypass the unbalanced battery pack system module or modules. A discharge switch within the battery pack system module may be used to prevent discharge current from passing through the battery cells of the battery pack system module when the bypass module switch is activated.

De-activation of the discharge switch in the battery pack system module prevents shorting of the battery cells in the battery pack system module, which would otherwise occur when the bypass module switch is activated. Because the discharge switch physically disconnects the battery cells from terminals of the battery pack system module and because there is no resistor in series with the bypass switch as in conventional battery balancing techniques, little to no power is dissipated during inter-module balancing when the bypass module switch is activated. The reduction in the dissipated power reduces heat generated in the battery pack system module, and reduces safety hazards experienced by the battery pack system and the operator of a device including the battery pack system.

The module bypass switch enables rapid balancing of battery pack system modules within a battery pack system without time-consuming and costly maintenance operations. Because the battery pack system modules are balanced during each charging of the battery pack system, the operation of the battery pack system presents reduced safety hazards to operators of equipment including the battery pack system. That is, over-charging of battery pack system modules within the battery pack system is reduced or eliminated, which reduces fire hazards in the battery pack system. Additionally, the balancing of the battery pack system modules through inter-module balancing during charging operations extends the life of the battery pack system modules and reduces replacements costs for operating equipment including the battery pack system module.

Balancing battery pack system modules through the module bypass switch allows balancing to occur faster than in conventional battery balancing techniques. Conventional battery balancing devices may re-direct charging currents on the order of hundreds of milliAmps. By providing a low resistance path through the module bypass switch, the magnitude of re-directed current may be many times higher, such as 10 to 100 Amps. Thus, when a battery pack system module is out of balance from other battery pack system modules in a battery system, the balancing operation is completed faster. For example, a balancing operation that may take several hundred hours under a conventional balancing system may be completed in several hours or less.

FIG. 2 is a circuit schematic illustrating an exemplary battery system module having charge, discharge, and bypass module switches according to one embodiment. Battery cells 212, 214, 216, and 218 are coupled in series with each other. Although not shown, additional battery cells may be coupled in series or in parallel with the battery cells 212, 214, 216, and 218. A positive battery terminal 202 and a negative battery terminal 204 are coupled with the battery cells 212, 214, 216, and 218. According to one embodiment, a load (not shown) may be coupled between the terminals 202 and 204 to receive an output voltage and/or output current from the battery cells 212, 214, 216, and 218.

According to another embodiment, the terminals 202 and 204 may be coupled to other battery pack system modules in parallel or series (as shown below with reference to FIG. 3). According to one embodiment, the battery cells 212, 214, 216, and 228 may be electrochemical cells such as lithium ion (Li-ion) battery cells, nickel-metal hydroxide (NiMH) battery cells, nickel cadmium (NiCd) battery cells, lead-acid battery cells, or a combination thereof. The battery cells may also include capacitors or super capacitors.

Balancing enable transistors 222, 224, 226, and 228 activate intra-cell balancing for each of the battery cells 212, 214, 216, and 218, respectively. For example, when balancing enable transistor 222 is activated the battery cell 212 may discharge through a resistor to balance with the battery cells 214, 216, and 218. Each of the balancing enable transistor 222, 224, 226, and 228 may be controlled through balancing enable signals 232, 234, 236, and 238, respectively. The balancing enable signals 232, 234, 236, and 238 may be controlled by a microprocessor 206. Further details of intra-module balancing within a battery pack system module is described in U.S. patent application Ser. No. 12/195,274 (published as U.S. Patent Application Publication No. 2008/0309288) entitled “Method for Balancing Lithium Secondary Cells and Modules” filed on Aug. 20, 2008, to Benckenstein et al., which is hereby incorporated by reference.

An analog controller 208 measures characteristics, current status, and voltages of the battery cells 212, 214, 216, and 218 through circuits 260, 262, 264, 266, and 268. According to one embodiment, the circuits 260-268 are a combination of a resistor and a capacitor such as an RC circuit. The analog controller 208 may be powered by the battery cells 212, 214, 216, and 218 through a line 284 and/or through an external charger (not shown) through a voltage regulator 258. The microprocessor 206 may enable or disable the balancing enable signals 232, 234, 236, and 238 by receiving information about the battery cells 212, 214, 216, and 218 from the analog controller 208 through a communication bus 242 such as an I²C bus. The microprocessor 206 may also receive information from the analog controller 208 through an analog signal 246. According to one embodiment, the microprocessor 206 is powered by a voltage regulator within the analog controller 208 through a line 278. The analog controller 208 may also monitor for short circuits within the battery cells 212, 214, 216, and 218.

According to one embodiment, the microprocessor 206 may issue commands to the analog controller 208 through the bus 242 for the analog controller 208 to output signals on the analog line 246 proportional to the output voltage of one of the battery cells 212, 214, 216, and 218 and read battery cell voltages from the analog line 246. An analog/digital converter (not shown) may be coupled between the microprocessor 206 and the analog line 246. The analog/digital converter may have a resolution selected to match a desired sensitivity for receiving voltages from the analog controller 208. For example, the analog/digital converter may be an 8-bit, 12-bit, 16-bit, 20-bit, or 24-bit converter. According to one embodiment, the microprocessor 206 may use information measured from the analog controller 208 in a gas gauging algorithm.

A zener diode 276 and a current limiting resistor 282 may be coupled between the terminals 202 and 204 to allow low current inter-module balancing between the battery pack system module 200 and other battery pack system modules (not shown). Further details of inter-module balancing with the zener diode 276 and current limiting resistor 282 is described in U.S. patent application Ser. No. 12/417,435 (published as U.S. Patent Application Publication No. 2009/0289599) entitled “System for Balancing a Plurality of Battery Pack System Modules Connected in Series” filed on Apr. 2, 2009, to White et al., which is hereby incorporated by reference.

A discharge switch 254 may be coupled in series with the battery cells 212, 214, 216, and 218 and the terminal 202. According to one embodiment, the discharge switch 254 is a field effect transistor (FET) having its body diode oriented to block discharge current from the battery cells 212, 214, 216, and 218. The discharge switch may be controlled by the analog controller 208.

A charge switch 252 may be coupled in series with the battery cells 212, 214, 216, and 218 and the terminal 202. According to one embodiment, the charge switch 252 is a FET having its body diode oriented to block charge current to the battery cells 212, 214, 216, and 218. The charge switch may be controlled by the analog controller 208. According to one embodiment, a driver 256 is coupled between the charge switch 252 and the analog controller 208.

A module bypass switch 240 may be coupled in parallel with the terminals 202 and 204 such that when the switch 240 is activated, substantially all current through the battery pack system module 200 flows through the switch 240. According to one embodiment, the switch 240 is a FET controlled by the analog controller 208. In another embodiment, the switch 240 is controlled by the microprocessor 206 through the analog controller 208. In yet another embodiment, the switch 240 is connected to the microprocessor 206 and receives commands directly from the microprocessor 206. In a further embodiment, the switch 240 is connected to the bypass detection circuit 272 and receives commands from the microprocessor 206 through the bypass detection circuit 272. The switch 240 may be activated when other battery pack system modules (not shown) in a battery pack system are unbalanced with the module 200. For example, when the battery pack system module 200 is charged to a higher level of charge than other battery pack system module coupled to the module 200, the module bypass switch 240 may be activated to supply charge current to other modules to bring the other modules into balance with the module 200. The microprocessor and/or the analog controller 208 may activate the switch 240 when a configurable voltage is measured across the terminals 202 and 204. The microprocessor 206 and/or the analog controller 208 may make decisions for operating the switch 240 with information received from a module bypass switch detection circuit 272, described below. Additionally, the microprocessor 206 and/or the analog controller 208 may forward commands to the switch 240 received through an external initializer, described below.

Inter-module balancing may be performed by de-activating the charge switch 252 to reduce to little or none the charging current flowing through the battery cells 212, 214, 216, and 218. After the charge switch 252 is de-activated inter-module balancing may be performed through the diode 276. Higher inter-module balancing currents may be obtained by activating the module bypass switch 240. Before the switch 240 is activated, the discharge switch 254 may be de-activated to prevent shorting of the battery cells 212, 214, 216, and 218. After de-activating the discharge switch 254, the module bypass switch 240 may be activated to allow charging current to bypass the module 200. After the module 200 has reached balance with other modules in the battery pack system, the module bypass switch 240 may be de-activated followed by activation of the charge switch 252 and of the discharge switch 254.

The charge switch 252, the discharge switch 254, and the module bypass switch 240 may be controlled through the analog controller 208 by the microprocessor 206. For example, the microprocessor 206 may issue commands over the bus 242 to activate or de-activate the switches 252, 254, and 240. The microprocessor 206 may issue commands to maintain balance between the battery pack system module 200 and other battery pack system modules. According to one embodiment, the microprocessor 206 is configured with information about the battery cells 212, 214, 216, and 218 and/or applications for using the module 200. For example, the microprocessor 206 may have information regarding open circuit voltage curves for and/or physical chemistry of the battery cells 212, 214, 216, and 218. According to another embodiment, the microprocessor 206 may have application information such as whether the module 200 is configured for use in a vehicle including load information. The microprocessor 206 may use the battery cell information and/or load information in determining operation of the switches 252, 254, and 240.

According to one embodiment, a Schottky diode 290 is coupled between the terminals 202 and 204. The Schottky diode 290 may prevent damage to the battery pack system module 200 from low voltage transients occurring at the terminal 202. The Schottky diode 290 may also carry bypass current from the terminal 202 to the terminal 204 before the switch 240 is activated. Further, a reverse voltage across the Schottky diode 290 may be measured by the microprocessor 206 and/or the analog controller 208 and used to decide when to activate the switch 240. According to another embodiment, a current-limiting transient voltage suppression (TVS) diode 292 is coupled between the terminals 202 and 204. The diode 292 may prevent damage to the battery pack system module 200 from high voltage transients at the terminal 202. According to another embodiment, the battery pack system module 200 may include both the Schottky diode 290 and the diode 292.

According to one embodiment, a fuse 270 is coupled in series between the discharge switch 254 and the battery cells 212, 214, 216, and 218. The fuse 270 prevents damage to the battery cells 212, 214, 216, and 218 in the event of a failure in the discharge switch 254.

The module bypass switch detection circuit 272 may be coupled in parallel with the module bypass switch 240. The detection circuit 272 may measure the voltage across the bypass module switch 240. According to one embodiment, the voltage is measured as the voltage between the terminals 202 and 204 and a battery voltage measured between the terminal 202 and the line 284. The module bypass detection circuit 272 may also detect reverse voltage conditions in the battery pack system module 200. When a low state of charge is reached in the battery pack system module, the discharge switch 254 may be de-activated to prevent over discharge of the battery pack system module 200. The diode 276 may allow discharge current to continue to pass through the battery pack system module 200 after the discharge switch 254 is de-activated. This may cause a reverse voltage to develop across the diode 276. The module bypass detection circuit 272 may detect the reverse voltage condition and activate the module bypass switch 240 to allow discharge current to pass through the battery pack system module 200. According to one embodiment, the diode 276 may be optional. In this embodiment, a reverse voltage may be measured across the Schottky diode 290 as described above.

The microprocessor 206 may also monitor the battery pack system module 200 through a thermistor 274 and a current sensing resistor 250. The thermistor 274 and the current sensing resistor 250 may be included in a pack sensing circuit. The thermistor 274 allows the microprocessor 206 to monitor the temperature of the module 200. The microprocessor 206 may use information about the temperature of the module 200 to activate or de-activate the module bypass switch 240, the charge switch 252, and/or the discharge switch 254 or combinations thereof. The microprocessor 206 may also use information from the current sensing resistor 250 to monitor the charge status of the battery cells 212, 214, 216, and 218. For example, the microprocessor 206 may perform Coulomb counting with the current sensing resistor 250. The microprocessor 206 may be coupled to the thermistor 274 and the current sensing resistor 250 through an analog-to-digital converter (not shown) selected to match a desired sensitivity for measurements.

The microprocessor 206 and the analog controller 208 may form a controller assembly. The controller assembly communicates through a bus 244. The bus 244 may be, for example, an RS-232 or RS-485 bus. According to one embodiment, the microprocessor 206 receives a module enable signal 248 to enable or disable the module 200. The bus 244 may be used by the microprocessor 206 and/or the analog controller 208 to report current measured from the current measurement resistor 250, to report over-charge or over-discharge currents, to report a temperature measured by the thermistor 274, to report Coulombs counted for the battery cells 212, 214, 216, and 218, and/or to report status of the charge switch 252, the discharge switch 254, and the module bypass switch 240.

According to one embodiment, the bus 244 includes isolation circuits (not shown). The isolation circuits may optically or digitally isolate a voltage on the bus 244 from voltages within the battery pack system module 200.

According to one embodiment, the microprocessor 206 may also receive a reset signal (not shown). The reset signal may be a separate line connection such as the module enable signal 248 or the reset signal may be received over the bus 244. The reset signal allows for restarting and/or troubleshooting the microprocessor 206. The microprocessor 206 may also include other debugging functionality available through the bus 244 or other line connection.

FIG. 3 is a block diagram illustrating an exemplary battery pack system having series and parallel coupled battery pack system modules according to one embodiment. A battery pack system 300 includes first modules 320 a, 320 b, . . . , 320 h coupled in series with each other. The system 300 also includes second modules 322 a, 322 b, . . . , 322 h, third modules 324 a, 324 b, . . . , 324 h, fourth modules 326 a, 326 b, . . . , 326 h, and fifth modules 328 a, 328 b, . . . , 328 h. Each of the modules of the second modules 322 are coupled in series with each other and the third modules 324, fourth modules 326, and fifth modules 328 are similarly coupled in series. The first modules 320, second modules 322, third modules 324, fourth modules 326, and fifth modules 328 are coupled in parallel between a negative terminal 302 and a positive charge terminal 304 and a positive discharge terminal 306. Diodes 308 a, 308 b, . . . , 308 e are coupled between the positive charge terminal 304 and the modules 320, 322, 324, 326, and 328. Diodes 310 a, 310 b, . . . , 310 e are coupled between the positive discharge terminal 306 and the modules 320, 322, 324, 326, and 328. The diodes 308 and 310 may be isolation diodes to prevent any of the first modules 320, second modules 322, third modules 324, fourth modules 326, and fifth modules 328 from discharging any other of the modules 320, 322, 324, 326, and 328.

Each of the modules of the first modules 320, second modules 322, third modules 324, fourth modules 326, and fifth modules 328 may include a module bypass switch as described above with reference to FIG. 2 and other balancing circuits as described in U.S. patent application Ser. No. 12/417,435. Inter-module balancing may be effected through the use of the module bypass switch in the modules 320, 322, 324, 326, and 328. For example, if the module 320 e is at a higher charge than the module 320 d, the module 320 e may de-activate a charge switch, de-activate a discharge switch, and activate a module bypass switch in the module 320 e to allow charge current to flow to the module 320 d. The current may also flow to the modules 320 a-c and 320 f-h that have not activated their module bypass switches through the series connection of modules 320. Control of inter-module balancing may be performed within each of the modules 320, 322, 324, 326, and 328 as described below with reference to FIG. 4 or by an initializer (not shown), by a client device (not shown), or by a master battery system pack module described below with reference to FIGS. 5 and 6.

The battery pack system 300 may be charged through a power supply (not shown) coupled to the positive charge terminal 304 and the negative terminal 302. According to one embodiment, the power supply may be a constant-current constant-voltage power supply. According to other embodiments, the power supply 332 may be a fuel cell, a solar cell, or combinations thereof.

Although FIG. 3 illustrates five parallel coupled groups of eight series connected battery pack system modules, a battery pack system may incorporate any number of battery pack system modules in series or parallel. The battery pack system modules in a battery pack system may be of similar capacity, similar output voltage, and/or similar output current, or have different capacities, different output voltages, and/or different output currents. Additionally, the diodes 308 and 310 of FIG. 3 may be coupled on a high potential or low potential end of the modules 320, 322, 324, 326, and 328.

According to one embodiment, the isolation diodes 308 and 310 may be removed and the modules 320, 322, 324, 326, and 328 are charged and discharged from a single port rather than the ports 304 and 306. In another embodiment, the modules 300, 322, 324, 326, and 328 may be connected in parallel through connections in between the port 302 and the ports 304 and 306. For example, the modules 320 g, 322 g, 324 g, 326 g, and 328 g may be coupled in parallel with each other. Likewise, one or more other sets of modules 320-328 a, 320-328 b, etc. may be coupled in parallel.

FIG. 4 is a flow chart illustrating an exemplary method of charging a battery pack system module according to one embodiment. A flow chart 400 begins at block 402 by determining if the battery pack system module has reached a first criteria. According to one embodiment, the first criteria is a level of charge. According to other embodiments, the first criteria may be a battery cell temperature, a battery cell voltage, or other measurable characteristics of the battery cell. If the first criteria is not reached, the flow chart returns to block 402 until the first criteria is met.

When the first criteria is reached, the charge switch is de-activated at block 404. At block 406, the voltage across the battery pack system module's terminals are determined to exceed a first voltage value. If the voltage across the battery pack system module's terminals has not exceeded a certain first voltage value, the flow chart returns to block 406. According to one embodiment, the first voltage value of block 406 may be determined from the voltage of the power supply, the voltage of the battery pack system modules in the battery pack system, and/or the number of battery pack system modules or a combination of these. The first voltage value may be configured as a value specific to a particular battery pack system configuration. After the charge switch voltage exceeds a certain voltage value, the discharge switch is de-activated at block 408 and a module bypass switch is activated at 410. Thus, charge current is allowed to pass through the battery pack system module through a low resistance path without discharging the battery cells of the module.

A timer may be started after activating the module bypass switch, and, when a certain time period has passed at block 412, the module bypass switch is de-activated at block 414. The charge switch and discharge switch may be re-activated at block 416.

According to one embodiment, the method 400 may be executing within a microprocessor or controller assembly in parallel with other processes. For example, other processes may monitor parameters such as temperature, state of charge, and charge or discharge current. The other processes may also issue commands to the charge switch, discharge switch, and/or module bypass switch. For example, one of the other processes may activate the charge switch while the method 400 is looping at block 406. In this example, the charge switch may be again de-activated at block 408.

The method of FIG. 4 provides for inter-module balancing of a battery system by allowing a battery pack system module to have autonomous control over charging of battery cells within each respective battery pack system module without communication to a central computer. According to another embodiment, the battery pack system module may be in communication with an initializer, such as a microcontroller, for controlling the balancing of battery pack system modules within a battery pack system. The method of FIG. 4 may be used in combination with a separate method for activating a module bypass switch executed by a bypass detection circuit, such as the bypass detection circuit 272 described above. When used in combination with a bypass detection circuit, a microprocessor programmed to perform the steps of FIG. 4 may allow a configurable voltage for activating a module bypass switch in addition to the voltage that activates the bypass detection circuit.

FIG. 5 is a block diagram illustrating an exemplary battery pack system having a plurality of battery pack system modules according to one embodiment. A system 500 includes a battery pack system 502 having battery pack system modules 504 a, 504 b, 504 c. The battery pack system module 504 a includes a controller assembly 510 for interfacing with a bus 540 and components within the battery pack system module 504 a. The controller assembly 510 may include analog controllers, digital controllers, and/or microprocessors. According to one embodiment, the battery pack system module 504 a includes an isolated bus interface 524 for isolating the battery pack system module 504 a from the bus 540, which may be operating at a different potential.

The controller assembly 510 may interface with a module bypass detector circuit 512 and module bypass switch 514. By sensing an output from the module bypass detector circuit 512, the controller assembly may determine when to activate and de-activate the module bypass switch 514 and a disconnect circuit 516. The disconnect circuit 516 may include a charge switch and a discharge switch. The controller assembly 510 may also interface with a pack sensing circuit 518 and the disconnect circuit 516. The pack sensing circuit 518 may report to the controller assembly 510 characteristics of battery cells (not illustrated) located within the battery pack system module 504 a. For example, the pack sensing circuit 518 may monitor charge levels of the battery cells with Coulomb counters or battery cell temperatures with thermistors. The coulomb counters and/or thermistors may interface with the controller assembly 510 through an analog/digital converter (ADC). The controller assembly 510 may use information obtained from the pack sensing circuit 518 to determine activation and de-activation of a charge switch and a discharge switch within the disconnect circuit 516.

Additionally, the battery pack system module 504 a may include an internal display 522 to communicate with an operator of the battery pack system 502 a status of the battery pack system module 504 a. For example, the battery pack system module 504 a may include a light emitting diode (LED) indicating the status of the module bypass switch 514. In another example, the internal display 522 may be a liquid crystal display (LCD) indicating the charge level of battery cells within the battery pack system module 504 a.

An initializer 542 coupled to the bus 540 may communicate with each of the battery pack system modules 504 a, 504 b, 504 c. The initializer 542 may accumulate information from each of the battery pack system modules 504 a, 504 b, 504 c to make decisions regarding the charging operation of the battery pack system modules 504 a, 504 b, 504 c. For example, by monitoring the charge levels of the different battery pack system modules 504 a, 504 b, 504 c, the initializer 542 may instruct an unbalanced battery pack system module to activate the module bypass switch. According to one embodiment, the initializer 542 may be coupled to an external display device (not shown) for displaying the status of the battery pack system 502 and/or receiving operator commands for the battery pack system 502. The initializer 542 may monitor the battery pack system 502 for one or more events such as, for example, health of the battery cells, capacity of the battery cells, overcharge, over discharge, over current, short circuit current, over temperature, under temperature, state of charge of the battery cells, and/or balance of the battery cells. According to one embodiment, the initializer 542 may be programmed with new computer instructions or configuration settings through, for example, a flash update to an EEPROM chip storing computer instructions in the initializer 542. In another embodiment, the initializer 542 may download new computer instructions and/or configuration data into the controller assembly 510.

According to one embodiment, the initializer 542 may have control of all internal cell balancing circuits within a module for intra-module balancing and low current precision inter-module balancing, as well as control over the module bypass switch for each of the modules for accurate high current inter-module balancing. Thus, the initializer may perform inter-module balancing and intra-module balancing. The combination of inter-module balancing and intra-module balancing allows continuous balancing in any battery mode including charge mode, discharge mode, quiescent mode, and storage mode. For example, the initializer 542 may activate all intra-module discharge balancing circuits in a module in order to balance the module with other modules.

The initializer 542 may be coupled to a network 544 for communicating with a client device 546. The initializer 542 may allow the client device 546 to monitor conditions within each of the battery pack system modules 504 a, 504 b, 504 c and/or control components within the battery pack system modules 504 a, 504 b, 504 c. For example, an operator at the client device 546 may instruct the initializer 542 to activate the module bypass switch 514 of the battery pack system module 504 a. In another example, an operator at the client device 546 may adjust settings within the initializer 542 such as current limits, voltage limits, temperature limits, charge levels, and/or balancing settings. In yet another example, an operator at the client device 546 may collect status and data from all of the battery pack system modules on the bus 540 for real-time continuous display of the complete battery system and for setting and resetting battery system audio and visual alarms.

According to one embodiment, the initializer 542 may be removed from the system 500 by designating the controller assembly 510 of the battery pack system module 504 a, or another one of the battery pack system modules 504 a, 504 b, 504 c, to function as a master controller. The master controller communicates with other battery pack system module controller assemblies and may provide access for an operator on a client device, an internal display, and/or an external display.

FIG. 6 is a block diagram illustrating a client device for an exemplary battery pack system according to one embodiment. A computer system 600 includes a central processing unit (CPU) 602 coupled to a system bus 604. The CPU 602 may be a general purpose CPU or microprocessor, graphics processing unit (GPU), microcontroller, or the like. The present embodiments are not restricted by the architecture of the CPU 602 so long as the CPU 602, whether directly or indirectly, supports the modules and operations as described herein. The CPU 602 may execute the various logical instructions according to the present embodiments. Logical instructions may be stored in the CPU 602, in a battery pack system module (not shown), or in an initializer (not shown).

The computer system 600 may also include random access memory (RAM) 608, which may be, for example, SRAM, DRAM, SDRAM, or the like. The computer system 600 may use RAM 608 to store the various data structures used by a software application having code to electronically monitor and control battery pack system modules. The computer system 600 may also include read only memory (ROM) 606 which may be PROM, EPROM, EEPROM, optical storage, or the like. The ROM may store configuration information for booting the computer system 600. The RAM 608 and the ROM 666 hold user and system data.

The computer system 600 may also include an input/output (I/O) adapter 610, a communications adapter 614, a user interface adapter 616, and a display adapter 622. The I/O adapter 610 and/or the user interface adapter 616 may, in certain embodiments, enable a user to interact with the computer system 600 in order to input operating parameters for a battery pack system module. In a further embodiment, the display adapter 622 may display a graphical user interface for monitoring and/or controlling battery pack system modules. The display adapter 622 or other user interface device on the bus 604 may include audio outputs and high visibility visual displays for audibly and/or visually alerting a user to battery system status; especially status that requires priority response from a user.

The I/O adapter 610 may connect one or more storage devices 612, such as one or more of a hard drive, a compact disk (CD) drive, a floppy disk drive, and a tape drive, to the computer system 600. The communications adapter 614 may be adapted to couple the computer system 600 to a network, which may be one or more of a LAN, WAN, and/or the Internet. The user interface adapter 616 couples user input devices, such as a keyboard 620 and a pointing device 618, to the computer system 600. The display adapter 622 may be driven by the CPU 602 to control the display on the display device 624.

The applications of the present disclosure are not limited to the architecture of computer system 600. Rather the computer system 600 is provided as an example of one type of computing device that may be adapted to perform the functions of a client device 546. For example, any suitable processor-based device may be utilized including without limitation, personal data assistants (PDAs), tablet computers, smartphones, computer game consoles, or multi-processor servers. Moreover, the systems and methods of the present disclosure may be implemented on application specific integrated circuits (ASIC), very large scale integrated (VLSI) circuits, or other circuitry. In fact, persons of ordinary skill in the art may utilize any number of suitable structures capable of executing logical operations according to the described embodiments.

External control of a battery pack system with an initializer may be performed when the initializer communicates with controller assemblies within the battery pack system modules. FIG. 7 is a flow chart illustrating an exemplary method of charging a battery pack system according to one embodiment. A flow chart 700 begins at block 702 where an initializer decides if a battery pack system module has become unbalanced with other battery pack system modules within a battery pack system. In one example, the battery pack system module may be determined to be charged to a higher level than other battery pack system modules in the battery pack system. If a battery pack system is unbalanced the flow chart continues to block 704. At block 704 the charge switch in the unbalanced battery pack system module may be de-activated to prevent further charging of battery cells within the unbalanced battery pack system module. Additionally, at block 704 the discharge switch is de-activated to prevent shorting of the battery cells when the module bypass switch is activated. At block 706 the module bypass switch for the unbalanced battery pack system module is activated.

At block 708 it is determined if the battery pack system modules have reached a balanced state with the unbalanced battery pack module. When balance is reached, the flow chart continues to block 710. At block 710 the module bypass switch for the previously unbalanced battery pack system module is de-activated. At block 712 the charge switch and the discharge switch for the previously unbalanced battery pack system module are activated. The method illustrated in FIG. 7 may be performed by an initializer, a client device, or a battery pack system module configured as a master module to control other modules. When the initializer, client device, or master module is coupled to a display or a client device, software may be executed to display a user interface for monitoring and/or controlling the battery pack system.

FIG. 8 is a block diagram illustrating a software application for monitoring a battery pack system according to one embodiment. A software application 800 may include displays 810, 820 for monitoring battery pack system modules inside of a battery pack system. The displays 810, 820 may include information such as, for example, temperature, charge level, voltage, status of the module bypass switch, and/or alerts (not shown) for each battery pack system module in the battery pack system. Additionally, the software application 800 may include buttons 812, 822 for activating module bypass switches within the battery pack system modules monitored in displays 810, 820, respectively. Charge switches and/or discharge switches may be activated and de-activated automatically by the software when the buttons 812 and 822 are actuated. According to one embodiment, the display also includes separate buttons 814 and 824 for activating and de-activating a charge switch of each module and buttons 816 and 826 for activating and de-activating a discharge switch of each module. The software application 800 may be stored on a computer readable medium such as, for example, a compact disc (CD), a hard disk drive (HDD), a digital versatile disc (DVD), flash memory, or the like.

The battery pack system of the present disclosure allows balancing of battery pack system modules within the battery pack system with a module bypass switch, charge switch, and discharge switch. The module bypass balancing process may be performed continuously during charging or discharging of the battery pack system modules resulting in increased life from the battery pack system modules and reduced safety hazards from unbalanced battery pack system modules. Balancing times may be reduced with the module bypass switch, charge switch, and discharge switch because of higher charging or discharging balancing current passing through the modules. The faster balancing times may be achieved with little or no additional heat dissipation in the battery pack system module. Reducing the heat dissipation prevents dangerous conditions from developing in the battery pack system module.

Faster balancing may be particularly advantageous when replacing battery pack system modules. For example, if one of the battery pack system modules is replaced, the replacement battery pack system module may be rapidly brought into balance with other battery pack system modules by activating module bypass switches, charge switches, and discharge switches to direct charge current to the unbalanced battery pack system modules.

According to another embodiment, the bypass current through the module bypass switch may be monitored and used to determine when to activate and/or deactivate the module bypass switch. FIG. 9 is a circuit schematic illustrating an exemplary battery pack system module having charge, discharge, and module bypass switches and bypass switch current monitoring according to one embodiment. A battery pack system module 900 is similar to the battery pack system module 200 of FIG. 2. However, the module bypass switch 240 is coupled to the current sensing resistor 250. When the module bypass switch 240 is activated current bypasses the battery cells 212, 214, 216, and 218. Instead, current flows substantially through the module bypass switch 240 and the current sensing resistor 250 from the terminal 202 to the terminal 204.

When bypass current flows through the current sensing resistor 250, the microprocessor 206 may measure a voltage across the current sensing resistor 250 and calculate a value for the magnitude of the bypass current. For example, the microprocessor 206 may receive a value from an analog to digital converter (not shown) coupled between the current sensing resistor 250 and the microprocessor 206. The microprocessor 206 may use information about the value of the bypass current flowing through the module bypass switch 240 to instruct the analog controller 208 to activate and/or de-activate the module bypass switch 240. Although the current sensing resistor 250 is illustrated in FIG. 9 for measuring bypass current through the module bypass switch 240, other current measurement devices may be used instead.

One method for programming the microprocessor 206 for monitoring the bypass current through a current measurement device is described with reference to FIGS. 10A-B. FIGS. 10A-B are a flow chart illustrating an exemplary method of charging a battery pack system module with bypass switch current monitoring according to one embodiment. A method 1000 begins at block 402 with determining if a battery pack system module has reached a first criteria. When the battery pack system module has reached a first criteria the method 1000 continues to block 404 with de-activating a charge switch.

The method 1000 continues to block 1006 with determining whether the voltage across the module bypass switch exceeds a first voltage value. If the module bypass switch has not exceeded the first voltage value, the flow chart returns to block 1006. After the module bypass switch voltage exceeds the first voltage value, the discharge switch is de-activated and the charge switch is de-activated at block 1008 and a module bypass switch is activated at block 1010. As described above, the charge switch may be de-activated at block 1008 after block 1004 because a separate process may have activated the charge switch. Thus, charge current is allowed to pass through the battery pack system module through a low resistance path without discharging the battery cells of the module.

At block 1020 the bypass current passing through the module bypass switch is measured. As long as the bypass current exceeds a threshold value the method 1000 remains at block 1020. When the bypass current falls below the threshold value another battery pack module in the series of battery pack modules may have opened its module bypass switch. By monitoring for this decrease in bypass current the battery pack system module may determine when it has reached a similar state of charge as other battery pack system modules it is in series with. For example, if any other battery pack system modules in series with the bypassed battery pack system module opens its charge switch this will result in stopping all charge current to all of the series connected modules with the exception of a moderate amount of 2 mA current to power the battery pack system modules' control circuits, in addition to a possible 150 mA current through the modules' zener diode bypass circuits (e.g., diode 276 and diode 282 of FIG. 2) and a possible 50 mA of current measurement error. In this example, an appropriate threshold value may be 202 mA (e.g., 2 mA+150 mA+50 mA). After the bypass current falls below the threshold value the method 1000 proceeds to block 1014 with de-activating the module bypass switch and to block 1016 with activating the charge switch and activating the discharge switch. Although not shown, a method of operating a microprocessor for monitoring bypass current may include additional steps as described above including, for example, remote monitoring of the bypass current.

According to one embodiment a microprocessor programmed according to the method 1000 may utilize additional information for making decisions regarding activating and/or de-activating the bypass current switch, the charge switch, and the discharge switch. For example, the microprocessor may utilize information such as an amount of time the module bypass switch has been activated in deciding when to activate or de-activate the module bypass switch.

Monitoring bypass current for controlling module bypass switch operation as described in FIGS. 9 and 10A-B may provide additional advantages over a timer based method as described in FIGS. 2 and 4. By monitoring the bypass current a battery pack system module may acquire information regarding other battery pack system modules coupled to it. The information inferred about other battery pack system modules through the bypass current monitoring does not require communications between the battery pack system modules, which may increase the cost and complexity of the battery pack system modules. When the battery pack system module has information about the state of charge of other battery pack system modules, the battery pack system module may make more informed decisions. In fact, the battery pack system modules may perform autonomous inter-module balancing by monitoring the bypass current through the module bypass switch.

The additional information and autonomous behavior may increase the speed and/or accuracy with which the battery pack system modules become balanced. For example, accuracy of inter-module balancing may improve from 10-15% error without bypass current monitoring to 2-3% with bypass current monitoring. Accuracy of the inter-module balancing refers to the difference in state of charge between battery pack system modules when the balancing process has completed. That is, without bypass current monitoring the inter-module balancing may only achieve a charge state for the battery pack system modules within 10% of each other. With bypass current monitoring, inter-module balancing may achieve a charge state for the battery pack system modules with 2% of each other.

By achieving a more accurate coarse balancing of the battery pack system modules a quicker balancing of the battery pack system modules may be obtained. After coarse balancing of the battery pack system modules through inter-module balancing with the module bypass switches of the battery pack system modules, fine balancing of the battery pack system modules follows to bring the battery pack system modules closer to a balanced state. Fine balancing is a slower process than coarse balancing and, thus, the more accurate balance obtained with coarse balancing the less time consumed for fine balancing mode. For example, considering battery pack system modules with a total capacity of 100 Amp-hours and a fine balancing rate of 100 milliAmps/hour, balancing battery pack system modules with fine balancing after coarse balancing achieves 10% accuracy may take one or more days. Balancing the same battery pack system modules with fine balancing after achieving 2% accuracy with inter-module balancing with current bypass monitoring may consume only a few hours. Thus, inter-module balancing with current bypass monitoring improves availability of battery pack system modules by decreasing the time consumed balancing the battery pack system modules.

Although the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods, and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the present disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. 

What is claimed is:
 1. An apparatus, comprising: a first battery pack system module, comprising: a battery cell coupled between a first terminal and a second terminal; a charge switch coupled in series with the battery cell and the first terminal for interrupting charging of the battery cell; a discharge switch coupled in series with the charge switch and the first terminal for interrupting discharging of the battery cell; a module bypass switch for shorting the first terminal and the second terminal; and a current measurement device coupled between the module bypass switch and at least one of the first terminal and the second terminal
 2. The apparatus of claim 1, further comprising a zener diode in series with a resistor, the zener diode and the resistor in parallel with the module bypass switch.
 3. The apparatus of claim 1, in which the module bypass switch is a field effect transistor (FET).
 4. The apparatus of claim 1, further comprising a second battery pack system module coupled in series with the first battery pack system module.
 5. The apparatus of claim 1, further comprising: a controller assembly coupled to the charge switch, the discharge switch, the module bypass switch, and the current measurement device; a bus coupled to the controller assembly; and an initializer coupled to the bus.
 6. The apparatus of claim 5, further comprising a pack sensing circuit coupled to the controller assembly.
 7. The apparatus of claim 5, further comprising a fuse coupled between the discharge switch and the battery cell.
 8. The apparatus of claim 5, further comprising an isolated bus interface coupled between the bus and the controller assembly.
 9. The apparatus of claim 5, in which the controller assembly is configured to monitor a bypass current through the module bypass switch by measuring the bypass current from the current measuring device. 